Fabrication of large-size Fe-based glassy cores with good soft magnetic properties by spark plasma sintering
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Akihisa Inoue Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Received 27 April 2003; accepted 10 June 2003)
Glassy Fe65Co10Ga5P12C4B4 alloy powders with a large supercooled liquid region of 50 K before crystallization were synthesized in the particle size range below 125 m by Ar gas atomization. With the aim of developing a large-size Fe-based glassy core with good soft magnetic properties, the consolidation method of spark plasma sintering was applied to the Fe65Co10Ga5P12C4B4 glassy powders. The existence of the supercooled liquid region enabled us to form a large-size glassy alloy disc 20 mm in diameter and 5 mm in thickness with a high relative density of 99.7% at the glass-transition temperature of 723 K and under the external applied pressure of 300 MPa. The resulting glassy core of 18 mm in outer diameter, 10 mm in inner diameter, and 4 mm in thickness exhibits good soft magnetic properties: 1.20 T for saturation magnetization, 6 A/m for coercive force, and 8900 for maximum permeability. The good soft magnetic properties of the Fe-based bulk glassy core are attributed to the combination of the high relative density and the maintenance of the single glassy structure.
I. INTRODUCTION
Since amorphous alloys in Fe-metalloid system were found to exhibit good soft magnetic properties in 1974,1–3 a large number of studies on the development of soft magnetic amorphous alloys have been carried out for the subsequent twenty years. However, the shape and dimension of the practical soft magnetic alloys had been limited to thin sheet with a thickness less than about 50 m and fine wire with a diameter less than 150 m. The limitation is due to the necessity of a high cooling rate for formation of an amorphous phase.4,5 The elimination of the limitation of the sample shape and dimension has been strongly expected because it will cause a more wide extension of application fields. Much effort has been devoted to prepare the samples, with desired shape and size by powder metallurgy.6–8 However, it was extremely difficult to produce the bulk samples such as magnetic core, because of the necessity of consolidation under tremendously high pressure at a lower temperature without crystallization.9–11 In addition, it was difficult to reduce sufficiently internal stress by annealing at low temperatures without crystallization. Consequently, new Fe-based amorphous alloys with high thermal stability and high deformability have been desired for formation of bulk samples. J. Mater. Res., Vol. 18, No. 9, Sep 2003
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Since 1995, various types of Fe- and Co-based bulk glassy soft magnetic alloys with a size above 1 mm in diameter were synthesized in Fe–(Al, Ga)–(P, C, B),12 Fe–(Nb, Cr, Mo)–(Al, Ga)–(P, C, B),13 Fe–Ga–(P, C, B),14 Fe–(Cr, Mo, Co)–Ga–(P, C, B),15–17 Fe–(Zr, Hf, Nb)–B,18 Fe–Si–B–(Nb, Zr),19, 20 Fe–Ga–(P, C, B, Si),21 Co–Fe–Nb–Ta,22 and Co–Fe–Si–B–Nb23 systems. It is characterized that all these Fe-based bulk glassy alloys exhibit a large
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